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March 07, 2014

In late February, the Hawaiian Electric Company (HECO) announced new technical standards for interconnecting residential photovoltaic (PV) systems onto its grid. The new standards specify the speed that the PV systems disconnect from the grid during a temporary voltage spike. The effect of these standards will be to will allow some neighborhoods in the HECO service territory to provide greater amounts of power generated by PV systems back to the utility grid than is consumed locally on sunny days.

Previously, HECO had limited its distribution transformers from supplying voltage upstream of the neighborhoods they serve. In some neighborhoods with a large number of solar systems, power generated by the rooftop PV panels was exceeding the power consumed in the area served by a particular transformer. HECO calls this threshold 100% daytime minimum load. The utility is concerned that exceeding this threshold would cause power flow in a different direction than grid was designed for, which might damage sensors or other power equipment needed to operate the power grid.

The new standards increase the requirements on power inverters that interconnect the rooftop PV systems to the power grid to limit what is called transient over-voltages. The net effect will be to increase the amount of power flowing back into the power grid to 120% of daytime minimum load. In other words, this increases the limit by 20% for neighborhoods with a relatively large number of solar systems. The new standards apply only to residential PV systems rated at less than 10 kilowatts.

HECO already ranks among the top ten utilities in the country for per capita solar installations. Read more about the utility’s solar program.